309 



a lack of iron. The authors named found jaundiced leaves turning green 

 where painted with a soluble iron salt. A change to green may also be ob- 

 served if the roots of such plants have a dilute iron solution at their disposal. 

 The experiments on the effectiveness of the iron solution were often re- 

 peated; as, for example, by Knop^ and Sachs-, who observed in cultures of 

 maize in nutrient solutions free from iron, that the plants remained green 

 only as long as the reserve material from the seeds lasted. After this time, 

 leaves developed which were green only at the tip and were already yellow 

 at the base, until the next leaves appeared uniformly icteric. Similar dis- 

 colorations, at first appearing in stripes, were found, on mature plants which 

 had developed normally at first, and then were placed in a nutrient solution 

 free from iron. The blossoms then became sterile and the production in dry 

 weight was considerably less. Frank=* observed that there occurred with a 

 lack of iron an universally noticeable phenomenon of starvation, viz., the 

 newly produced leaves exhausted the older ones, which lost their color and 

 died. In icteric organs, the chlorophyll grains have a normal form, but their 

 number and size is possibly smaller and their color pale. Although the 

 chlorophyll pigment contains no iron*, the whole nutritive condition of the 

 chlorophyll grain will become weakened by the lack of iron. But at first 

 ihe chloroplast exists in a normal form which is not destroyed until later. In 

 this lies the difference between the phenomena of starvation and enzymatic 

 albication. 



In order not to be obUged to separate the phenomena whose similar 

 symptoms lead to confusion, we will mention here icterus due to cold. We 

 find in cold, wet seasons a gradual yellowing in most cultivated plants, which 

 disappears of itself with a rise in temperature. Often in spring, the leaf 

 points of our flowering bulbs are yellow when they push out of the earth 

 and the young leaves push out gradually with a normal green color only as 

 the weather becomes warmer. 



From this transitory jaundice must be distinguished the chronic form, 

 in which the yellow leaves always remain yellow. This may be observed if 

 sudden great cold affects the young cells and destroys the chloroplasts. 

 Then, in place of these, are found only fine grained yellowish groups and 

 at times also yellow drops. These cells do not recover later. At the place 

 of transition to the parts of the leaves which, protected by the earth, have 

 become green, colorless, swollen and also light green chlorophyll grains 

 which later partly turn green may be found at the place of transition to the 

 portions of the leaf, which, protected by the earth, have become green. 



1 Knop (Jahresberichte f. Agriculturchemie, 1868-69, p. 288) observed in such 

 experiments that the iron which got into the plant could not be proved in the cell 

 sap, and, therefore, must be present in a combined form. In 1860 (Bot. Z. p. 357), 

 Weiss and Wiesner determined that iron occurs only in insoluble compounds and 

 in the contents of the older cells as well as in their walls. 



2 Experimentalphysiolog-ie, p. 144. 



3 Krankheiten der Pflanzen. 1895, I, p. 290. 



i Molisch, Die Pflanzen in ihren Beziehungen zum Eisen. 1892, p. 81. 



